1. Field of the Invention
This invention relates to a plasma downstream processing apparatus and a plasma downstream processing method, and more particularly to a plasma downstream processing apparatus and a plasma downstream processing method adapted for ashing an organic resist or for isotropic etching process used in manufacture of a semiconductor device, and having a high processing speed and giving less damage to the object to be processed.
2. Description of the Related Art
Recently, such a plasma downstream processing technique which can perform the processing at a high precision and give less damage to the substrate to be processed is increasingly demanded along with the high integration of a semiconductor integrated circuit device.
More specifically, high processing speed and less damage in the object to be processed is demanded in an ashing process for an organic resist and in an etching process for an insulating film. Plasma downstream processing would be promising in this regard.
FIG. 4 shows a conventional shower head type ashing apparatus. An ashing apparatus 50 comprises an aluminum housing 51 which defines an inner space. A microwave transmitting window 52 made of quartz is disposed in the housing 51 and hermetically couples to the inner surface of the housing, to define a microwave Introduction chamber 61 thereabove. A waveguide 54 for transmitting microwave is connected to the microwave Introduction chamber 61 and supplies microwave thereto.
The housing 51 and the microwave transmitting window 52 define an evacuatable hermetic space below the microwave transmitting window 52. A shower head 55 is disposed parallel to the microwave transmitting window 52 and coupled to the inner wall of the housing 51. A plasma generating chamber 64 is defined between the microwave transmitting window 52 and the shower head 55. A gas supply tube 53 is connected to the plasma generating chamber 64. A downstream processing chamber 68 is defined in the housing 51 below the shower head 55. The downstream processing chamber 68 contains a susceptor 60 which is provided with a heater 61.
Most of the constituent parts of the ashing apparatus 50, except the microwave transmitting window 52 and sealing members, are formed of aluminum. A substrate 59 to be processed, such as silicon wafer having an organic resist film thereon is mounted on the susceptor 60.
An O.sub.2 containing gas is introduced from the gas introducing tube 53 to the plasma generating chamber 64 and microwave is introduced from the waveguide 54 through the microwave introduction chamber 61 to the plasma generating chamber 64, to generate plasma of the O.sub.2 containing gas.
By the action of the plasma, oxygen radicals, which are the neutral and reactive species, together with electrons and ions are generated. These oxygen radicals are to be introduced into the processing chamber 68 through the shower head 55. The introduced oxygen radicals are transported downward and irradiated onto the surface of the substrate 59 mounted on the susceptor 60. The organic resist film coated on the substrate 59 is ashed by the irradiated oxygen radicals.
The shower head 55 is formed of a metal plate having a multiplicity of through holes, and is usually called a punching metal. Each through hole has a diameter of about 1 mm and a length (thickness) of the order of 2-3 mm. The O.sub.2 containing gas cannot go above the microwave transmitting window 52. The microwave cannot enter below the shower head 55. Since the through holes in the shower head 55 is small in diameter, plasma generated in the plasma generating chamber 64 is confined in the chamber 64 and cannot enter the processing chamber 68. Charged particles such as electrons and ions also confined in the plasma generating chamber.
Except the microwave transmitting window 52, most of the plasma generating chamber and the processing chamber are formed of aluminum which is a metal capable of shielding microwave and generating no contamination. During the ashing treatment, the inner wall of the ashing chamber 68 becomes 200.degree.-300.degree. C. due to the influence of the plasma in the plasma generating chamber 64, and the shower head 55 becomes hotter.
When the temperature of the metal inner surfaces of the respective chambers becomes hot, the possibility of annihilating oxygen radicals by the collision with the inner wall increases. Therefore, the radical concentration decreases and the ashing rate decreases. The decrease in the ashing rate also means a variation in the ashing rate and accompanies a decrease in the controlling accuracy.